The present invention relates to SiH Rhodium catalyzed composition and more particularly the present invention relates to SiH rhodium complex catalyzed compositions in which there is present an inhibitor compound which gives the composition good shelf life and allows it to cure at elevated temperatures in a short period of time. Release coatings for cellulosic substrates such as paper release coatings, as well as release coatings for plastic and metal substrates are well known. The substrate whether it be paper or a layer of plastic is coated with a release coating so that adhesive materials will stick to the substrate with great difficulty. One use of such paper release coatings and plastic release coatings is to utilize the paper release coated material for pressure sensitive adhesives. The paper release material is simply applied over the pressure sensitive adhesive allowing the article to be wound, and sold in that manner. For instance the paper release article may be applied as an interlayer over pressure sensitive adhesive tape to allow the tape to be rolled up. When it is desired to utilize the tape, the paper release layer is simply stripped off and the pressure sensitive adhesive tape is made to be used. The paper release layer can be removed from the pressure sensitive adhesive without a great deal of difficulty because of the paper release coating on the paper. Such coatings can be applied for similar uses on plastic and metal substrates. It has been found that for such uses silicone paper release coatings are especially suitable. The advantages of silicone paper release coatings are that they tend to be relatively non-toxic, have good high temperature stability and resistance to ultraviolet rays and also have good release properties. Of the silicone paper release coatings, two types had found wide usage, that is a paper release coating comprising the reaction product of a vinyl containing polysiloxane, a silicone hydride and a platinum catalyst and a paper release coating which is the reaction product or the cured product of a silanol containing polysiloxane, a silicone hydride and a tin catalyst. To be utilized in the commercial coating of paper, such paper release coatings have to be able to have a pot life of 12 hours or more, that is the material should not increase in viscosity more than 50% at room temperature over a 12 hour period and should cure in generally 5 to 60 seconds and more preferably 5 to 30 seconds at a temperature in the range of 300.degree. to 500.degree. F.
Traditionally, such compositions, that is either the platinum catalyzed compositions or tin catalyzed compositions, were applied in the form of a solution or a water based emulsion on the paper or substrate to be rendered releasable. For the tin system, such was a necessity since the desired shelf life could not obtained with the tin system, unless the composition was diluted in water or a solvent. Without dilution the tin system would generally cure or jell up in the container after being mixed prior to application to the paper in a relatively short period of time, typically less than an hour.
It should be noted that it was also envisioned utilizing the system consisting of a silanol-containing polysiloxane, silicone hydride crosslinking agent and a platinum catalyst. However, in such a system it was desirable to use a tin catalyst since it is considerably less expensive than the platinum catalyst.
With respect to the vinyl system, which was cured with a platinum catalyst, such a system in an emulsion form worked appropriately. An Example of a vinyl system which is cured with a platinum catalyst is for instance to be found in Moeller U.S. Pat. No. 4,066,594. However, the solvent and water-based emulsion systems for paper release coatings have two main disadvantages. With respect to the solvent systems, the evaporation of a solvent was required when the system was cured which solvent could not be released to the atmosphere in certain geographical areas due to pollution control requirements. As a result such solvent systems required the use of expensive equipment to collect the solvent as it was evaporated such that it would not be released to the atmosphere. With respect to the emulsion water-based systems in order for such systems to be cured, the water had to be evaporated first at high oven temperatures; only then the system would undergo the desired crosslinking reaction. Such evaporation of the water carrier resulted in the expenditure of a large amount of energy. Accordingly, at present there is an emphasis on desirably utilizing in paper release applications silicone systems which do not utilize a solvent or do not utilize a water carrier and in which the silicone system is applied at 100% solids. An example of a solvent-less silicone system which is disclosed to be utilized at 100% solids and which can be cured with a platinum catalyst or in the case of the silanol system with a tin catalyst is to be found in Grenoble U.S. Pat. No. 4,071,644.
In the case of the vinyl system disclosed in the foregoing Grenoble U.S. Pat. No. 4,071,644, most platinum catalysts are sufficient to cure the system at 100% solids. In the case of the silanol system which is cured with a silicon hydride it has been found that most platinum catalysts will effectively cure the system at elevated temperatures at a rapid enough rate to be commercially acceptable. On the other hand, the tin catalyst which will cure the system at an effective enough rate is undesirable in that in spite of all inhibitors that may be added to such a system, the system still does not have so long a shelf life as would be commercially desirable, that is a shelf life of 12 to 24 hours without gelling. It should be noted that the silianol system, that the system containing a silanol-containing polysiloxane, silicone hydride and a platinum or tin catalyst system is to be preferred over the vinyl system which is cured with a platinum catalyst since the silanol polysiloxane is much cheaper and easier to produce than the vinyl-containing polysiloxane. Accordingly, a number of attempts have been made to arrive at a good 100% solids silanol SiH paper release coating system with the appropriate cure rate at elevated temperatures and with good pot life at room temperature. In U.S. Pat. No. 3,992,433 there is disclosed a silanol polysiloxane SiH system for paper release coating utilizing a specific platinum catalyst as disclosed in the patent and specifically in Column 2. The large number of platinum catalysts disclosed in that patent, most of such platinum catalyst which are quite complex, will not cure the 100% solids silanol system at a sufficient rate at elevated temperatures. Accordingly, it was desirable to find an alternate catalyst and an inhibitor system which would result in a silanol system with good pot life at room temperature but with optimum curing speed at elevated temperatures, that is in the temperature range of 300.degree. to 500.degree. F. for a curing period varying from 5 to 60 seconds. It is also desirable not to be totally dependent on a few specific platinum catalysts as catalysts for silanol silicone hydride paper release coating systems. Recently, as disclosed in U.S. Pat. No. 3,928,629, rhodium complex catalysts have been disclosed as catalysts for vinyl polysiloxane, silicone hydride paper release coating systems. As stated in that patent, the rhodium complex catalyzed vinyl systems have desirable shelf life without an inhibitor and will cure the system at commercial paper coating rates. Another recent disclosure is U.S. Pat. No. 4,026,835, which it is disclosed that rhodium complex catalysts may be utilized as catalysts in the production of silicone foams by the reaction of silanol containing polysiloxanes with silicone hydrides.
It should be noted that with respect to the vinyl containing polysiloxane systems which were cross-linked with a silicone hydride and catalyzed with a rhodium complex, that such systems were not found to have as desirably as long a shelf life without an inhibitor. The types and kinds of inhibitors are not disclosed or discussed in U.S. Pat. No. 3,928,629. In addition U.S. Pat. No. 4,026,835 does not discuss whether that system that is disclosed in that patent could be applied to other than the production of silicone foams. Accordingly, it was highly desirable to be able to devise 100% solids silanol containing polysiloxane, silicone hydride rhodium complex catalyzed systems which would have a good pot life at room temperature and which would cure the silanol system at a sufficient rate of time in commercial coating techniques.
Accordingly, it is one object of the present invention to provide for 100% solids silanol SiH coating system.
It is another object of the present invention to provide for a solventless silanol SiH system which is catalyzed with a rhodium complex. It is an additional object of the present invention to provide for a 100% solids paper release coating system comprising a silanol polymer, silicone hydride, and a rhodium complex and an inhibitor compound, such that the system would have a good pot life at room temperature and cure at a sufficient rate at elevated temperatures.
It is yet another object of the present invention to provide 100% solids release coating composition comprising a silanol containing polymer, a silicone hydride, a rhodium complex and an inhibitor compound, a low molecular weight silanol containing diorganopolysiloxane polymer.
These and other objects of the present invention are accomplished by means of the disclosures set forth hereinbelow.